JP4367403B2 - Spring member for acceleration sensor, acceleration sensor, and magnetic disk drive device - Google Patents

Description

  The present invention relates to a spring member for an acceleration sensor using a magnetoresistive effect (MR) element, an acceleration sensor, and a magnetic disk drive apparatus including the acceleration sensor.

  For example, in a hard disk drive (HDD) incorporated in a portable device such as a portable personal computer, a cellular phone, a digital audio player, or a magnetic disk drive device such as an HDD or a removable HDD that is carried as a storage device, a magnetic field is generated by a drop impact. In order to prevent the head and the magnetic recording medium from colliding with each other, it is necessary to detect the moment when the head is dropped and to retract the magnetic head from the surface of the magnetic recording medium. Such a moment of falling can be detected as a slight change in gravitational acceleration.

  As an acceleration sensor for detecting slight changes in gravitational acceleration, a piezoelectric element type acceleration sensor that detects a change in force applied from a weight to a spring by supporting the weight with a spring and attaching a piezoelectric element to the spring. Is known (for example, Patent Document 1).

  As an acceleration sensor that detects a change in gravitational acceleration by a minute displacement of a weight, a capacitive acceleration sensor that detects a change due to the acceleration of the distance between a movable electrode and a fixed electrode facing each other as a change in these capacitances is also known. (For example, Patent Document 2).

  Such a piezoelectric element type acceleration sensor and a capacitance type acceleration sensor all need to be provided with an electrode for taking out a signal on the spring itself, on the weight attached to the spring or in the vicinity thereof, and therefore the wiring is routed. The structure becomes very complicated. In addition, applying fine wiring to a miniaturized spring or weight causes damage when an excessive impact is applied, and hinders displacement of the spring, which is an obstacle to improving sensitivity. This tendency becomes more remarkable as the acceleration sensor as a whole is miniaturized.

  As an acceleration sensor that can eliminate the above-mentioned disadvantages of conventional piezoelectric element type acceleration sensors and capacitance type acceleration sensors, it is supported by four stays that are easy to torsionally and flexibly deform, and is a three-dimensional torsion. A permanent magnet with a mass point that includes an axis on the Z axis is attached to a vibrator that can vibrate with four axes, and each has a center on a concentric circle around the origin of the coordinate axis on the X and Y axes. The above MR elements are arranged, and the change in the magnetic field intensity from the permanent magnet is caused by the relative difference between the output voltages of the two MR detection elements on the X axis, and the two MRs on the Y axis in the X axis direction. There has been proposed an acceleration sensor that detects acceleration in the Y-axis direction based on the relative difference between the output voltages of the detection elements and in the Z-axis direction based on the sum of output voltages of all MR detection elements (for example, Patent Document 3).

Japanese Patent No. 2732287 Japanese Patent No. 2586406 Japanese Patent Laid-Open No. 11-352143

  In the acceleration sensor described in Patent Document 3, a permanent magnet is fixed to a vibrator supported by four stays, that is, springs, and the rotational moment generated by the applied acceleration is balanced by the torsional stress of these stays. The acceleration is detected from the angle change of the permanent magnet at that time.

  In general, the spring coefficient of torsional stress in a leaf spring is larger than the spring coefficient of bending stress, and therefore its displacement is small. For this reason, when using a spring that mainly uses torsional stress as in the acceleration sensor described in Patent Document 3, it is difficult to increase the acceleration detection sensitivity because the amount of displacement is small. In order to increase sensitivity by increasing the amount of displacement, it is necessary to increase the overall spring area, which is contrary to the demand for miniaturization of the acceleration sensor.

  Therefore, an object of the present invention is to provide a spring member for acceleration sensor, an acceleration sensor, and an acceleration sensor capable of performing highly sensitive acceleration detection even when the acceleration sensor can be greatly reduced in size and reduced in size. An object of the present invention is to provide a magnetic disk drive device provided.

  According to the present invention, there is provided a spring member for an acceleration sensor to which a magnetic field generating means or a magnetic field detecting means that also serves as a weight member is attached, and is configured such that the weight member is attached to a position that has a fulcrum and deviates from the fulcrum. There is provided a spring member for an acceleration sensor provided with at least one strip-shaped leaf spring that generates a bending stress with respect to a force applied from the outside to displace the weight member.

  Since a strip-shaped leaf spring that displaces the weight member by generating and balancing a bending stress against the external force is used, the spring structure is small and has a large amount of displacement. A small and highly sensitive acceleration sensor can be provided.

  It is preferable that at least one belt spring is composed of two belt springs, and each belt spring has a fulcrum at one end and a weight member attached to the other end.

  It is also preferable that at least one strip-shaped leaf spring is composed of one strip-shaped leaf spring having a fulcrum at the center and a weight member attached to both ends.

  According to the present invention, there is further provided a spring member for an acceleration sensor to which a magnetic field generating means or a magnetic field detecting means also serving as a weight member is attached, the first belt spring having a fulcrum at the center, and the first belt shape. Two leaf-shaped leaf springs having a central portion connected to both ends of the leaf spring, respectively, and weight members are respectively attached to both ends of the second belt-like leaf spring. The first belt spring is configured to displace the weight member by generating a bending stress or a torsional stress with respect to a force applied from the outside, and the second belt spring is applied from the outside. A spring member for an acceleration sensor configured to generate a bending stress with respect to a force and displace the weight member is provided.

  Here, since a strip-shaped leaf spring is used to displace the weight member by generating and balancing mainly bending stress against external force, the spring structure is small and has a large amount of displacement. Thus, a small and highly sensitive acceleration sensor can be provided.

  Further, each of the two second belt springs is fixed to a weight member attached to each end of each second belt spring or each of the second belt springs, and the belt support for suppressing the spring action of each second belt spring. It is preferable to further include a member.

  According to the present invention, it further includes a housing member, a magnetic field generating weight member, a spring member having a fulcrum attached to the housing member, and a magnetic field detection sensor attached to the housing member so as to face the magnetic field generating weight member. And the spring member is fixed to the magnetic field generating weight member at a position deviated from the fulcrum, and at least one belt-like member that generates a bending stress with respect to an externally applied force to displace the magnetic field generating weight member. An acceleration sensor having a leaf spring is provided.

  As the spring member, a belt-like plate spring that displaces the weight member by generating and balancing a bending stress against an external force is used, and thus a small and highly sensitive acceleration sensor can be provided. Of course, since it is not necessary to provide electrodes on the spring member and the magnetic field generating weight member, the wiring structure is simplified. Further, since it receives a bias magnetic field from the magnetic field generating weight member, it is hardly affected by an external electric field and an external magnetic field.

  At least one strip-shaped leaf spring of the spring member is composed of two strip-shaped leaf springs, and each strip-shaped leaf spring has a fulcrum at one end and a magnetic field generating weight member is attached to the other end. Preferably it is.

  It is also preferable that at least one strip-shaped leaf spring of the spring member is composed of one strip-shaped leaf spring configured to have a fulcrum at the central portion and to be attached with magnetic field generating weight members at both ends.

  The magnetic field detection sensor includes a magnetization fixed layer and a magnetization free layer, and the magnetization fixed layer includes at least one pair of multilayer structure MR elements in which magnetization is fixed in a direction parallel to a displacement direction of at least one strip-shaped leaf spring, The generating weight member includes at least one permanent magnet, and is configured such that when a force is not applied from the outside, a magnetic field is applied in a direction substantially perpendicular to the laminated surface of at least one pair of multilayer structure MR elements. Preferably it is.

  According to the present invention, the housing member, the four magnetic field generating weight members, the spring member having a fulcrum attached to the housing member, and the housing member facing at least three of the four magnetic field generating weight members. Each having at least three magnetic field detection sensors attached thereto, the spring member having a first strip-shaped leaf spring having a fulcrum at the central portion, and the central portion being coupled to both ends of the first strip-shaped leaf spring. And two magnetic field generating weight members are attached to both ends of the two second belt springs, respectively, and the first belt spring is externally provided. It is configured to generate a bending stress or a torsional stress with respect to an applied force to displace the magnetic field generating weight member, and the second strip leaf spring generates a bending stress with respect to an externally applied force. Let me An acceleration sensor that is configured to displace the field generation members with weights is provided.

  Here, as the spring member, a strip-shaped plate spring that displaces the weight member by mainly generating and balancing a bending stress against an external force is used, so that a small and highly sensitive acceleration sensor can be provided. . If the four end portions of the two second strip-shaped leaf springs or strip-shaped support members have the same shape, it is possible to provide an acceleration sensor having the same X-axis, Y-axis, and Z-axis sensitivity and directivity. Of course, since it is not necessary to provide electrodes on the spring member and the magnetic field generating weight member, the wiring structure is simplified. Further, since the magnetic field detection sensor receives a bias magnetic field from the magnetic field generating weight member, it is not easily influenced by the external electric field and the external magnetic field.

  In addition, the magnetic field detection sensor includes a magnetization fixed layer and a magnetization free layer, and the magnetization fixed layer is at least one pair of multilayer structure MR elements in which the magnetization is fixed in a direction parallel to the displacement direction of the strip leaf spring. The magnetic field generating weight member includes at least one permanent magnet, and when a force is not applied from the outside, a magnetic field is applied in a direction substantially perpendicular to the laminated surface of at least one pair of multilayer structure MR elements. It is preferable that it is comprised so that. Since the magnetization fixed layer is magnetization fixed in the direction parallel to the displacement direction of the strip-shaped leaf spring, only the change of the bias magnetic field in this direction is detected by the multilayer MR element, The acceleration in the Y-axis direction can be detected independently. Further, since the magnetic field detection sensor uses a multilayer structure MR element including a magnetization fixed layer and a magnetization free layer, for example, a giant magnetoresistance effect (GMR) element or a tunnel magnetoresistance effect (TMR) element, magnetization vector detection is performed. The direction and magnitude of acceleration in each direction to be detected can be detected by one magnetic field detection sensor. Therefore, since the number of magnetic field detection sensors can be reduced and the structure can be greatly simplified, the acceleration sensor can be miniaturized. Further, since the GMR element and the TMR element have extremely high magnetic detection sensitivity, it is possible to perform highly sensitive acceleration detection. Furthermore, since it has a lower impedance than a piezoelectric element type acceleration sensor or a capacitance type acceleration sensor, it is less susceptible to disturbances.

  Each of the two second belt springs is fixed to two magnetic field generating weight members attached to both ends of each second belt spring or each of the second belt springs, and suppresses the spring action of each second belt spring. It is preferable to further include a belt-like support member.

  It is also preferable that at least one permanent magnet is composed of a pair of permanent magnets arranged in parallel so that the surfaces facing the magnetic field detection sensor have opposite polarities.

  It is also preferable that at least one pair of multi-layered MR elements are respectively arranged to face a pair of permanent magnets.

  The multilayer structure MR element is preferably a GMR element or a TMR element.

  According to the present invention, there is further provided a magnetic disk drive device provided with the acceleration sensor described above.

  According to the present invention, since the strip-shaped leaf spring that displaces the weight member by generating and balancing the bending stress against the external force is used, the spring structure is small and has a large displacement, and thus is small and highly sensitive. Thus, a small and highly sensitive acceleration sensor can be provided.

  FIG. 1 is a perspective view schematically showing an overall configuration of an example of a magnetic disk drive device incorporating an acceleration sensor. This magnetic disk drive device is an ultra-small HDD using a magnetic disk of 2.5 inches, 1.8 inches, 1.3 inches or 1 inch or less, for example, a portable personal computer, a mobile phone, a digital audio player, etc. The HDD incorporated in the portable device or the HDD itself or a removable HDD carried as storage.

  This figure shows a state in which the lid of the magnetic disk drive device is removed, 10 is a magnetic disk that is rotated by a spindle motor during operation, 10a is a retreat zone in which no data is written, and the magnetic head moves when a drop is detected, 11 Is a head gimbal assembly (HGA) having a magnetic head facing the surface of the magnetic disk 10 during operation, 12 is a flexible circuit (FPC) which is a wiring member electrically connected to the magnetic head, and 13 is an HGA 11. A support arm 14 for supporting, a voice coil motor (VCM) which is an actuator for positioning the support arm 13 by rotating the support arm 13 around the rotation shaft 15, and 16 a claw 13 a of the support arm 13 rides on when a fall is detected. A retraction lamp for separating the magnetic head from the surface of the magnetic disk, 17 is a circuit board 18 Respectively show the mounted acceleration sensor.

  FIG. 2 is an exploded perspective view schematically showing the overall configuration of one embodiment of the acceleration sensor of the present invention, and FIG. 3 is a configuration of a spring member, a magnetic field generating weight member, and a magnetic field detection sensor chip provided inside the housing member. It is a disassembled perspective view which shows schematically.

  As shown in these drawings, the acceleration sensor in the present embodiment is for detecting three-axis acceleration in the X-axis direction, the Y-axis direction, and the Z-axis direction. The spring member 21 formed integrally with the leaf spring 21a, the two second belt-like leaf springs 21b and 21c, and the four weight support portions 21d to 21g for supporting the magnetic field generating weight member, and the extension of the permanent magnet Four magnetic field generating weight members 22a to 22d having the same configuration such as size, shape and weight except for the direction, the first magnetic field detection sensor chip 23 for the X axis and the Z axis, and the X axis and the Z axis The second magnetic field detection sensor chip 24, the Y-axis third magnetic field detection sensor chip 25, and the fulcrum member 26 are accommodated.

  The housing member 20 includes a wiring board 20a formed by providing a wiring pattern (not shown) on a flat board made of a resin material such as polyimide or BT resin, and the housing member 20 covers and covers the wiring board 20a. And a cover member 20b formed of a magnetic metal material. In the present embodiment, it is possible to detect the three-axis acceleration in the X-axis direction, the Y-axis direction, and the Z-axis direction with the three magnetic field detection sensor chips 23 to 25 mounted on one plane by the wiring board 20a.

  In this embodiment, the spring member 21 is integrally formed by processing a thin metal plate made of NiFe or Ni, a thin plate made of stainless steel, or a thin resin plate made of polyimide or the like as shown in FIG. Is formed.

  The first strip-shaped plate spring 21a constitutes a main spring, and generates a bending stress and / or a torsional stress with respect to an externally applied force. The central part of the first strip-shaped leaf spring 21a constitutes a fulcrum, and this central part is fixed to the other end of the fulcrum member 26 whose one end is fixed to the wiring board 20a. The two second strip-shaped leaf springs 21b and 21c constitute a secondary spring and generate only a bending stress with respect to an externally applied force. The center portions of the second belt springs 21b and 21c are integrally connected to both ends of the first belt spring 21a. Both ends of the second belt springs 21b and 21c are integrally connected to weight support portions 21d to 21g having the same shape. The weight support portions 21d to 21g are rectangular in the figure, but may be circular or other shapes.

The magnetic field generating weight members 22a to 22d are fixed with adhesives on one surface of the weight supporting portions 21d to 21g of the spring member 21 (the surface opposite to the surface facing the magnetic field sensor chip). Magnetic field generation members with weights 22a~22d are each composed, permanent magnets 22a ₁ and _22a 2 of the pair of magnetic field generating, 22b ₁ and _22b 2, 22c ₁ and 22c _2, and from 22 d ₁ and 22 d _2.

  The first magnetic field detection sensor chip 23 for the X axis and the Z axis, the second magnetic field detection sensor chip 24 for the X axis and the Z axis, and the third magnetic field detection sensor chip 25 for the Y axis include four magnetic field generating weight members. The three magnetic field generating weight members 22a to 22c of 22a to 22d are respectively opposed to each other, more specifically, the other surfaces of the weight support portions 21d to 21f are respectively opposed to each other and fixed to the wiring board 20a with an adhesive. Has been. Therefore, the magnetic field generating weight members 22a to 22c apply magnetic fields whose angles change according to the acceleration to the first to third magnetic field detection sensor chips 23 to 25, respectively. In the present embodiment, the magnetic field generating weight member 22d is provided only for the purpose of maintaining the balance of the spring member 21.

The pair of permanent magnets 22a ₁ and 22a ₂ is formed of a rectangular parallelepiped ferrite material extending parallel to each other in the X-axis direction, and faces the first magnetic field detection sensor chip 23 for the X-axis and Z-axis. Yes. The pair of permanent magnets 22a ₁ and 22a ₂ are arranged so that the surfaces facing the first magnetic field detection sensor chip 23 have opposite polarities, and they constitute a closed magnetic circuit. As will be described later, the spin valve GMR element of the first magnetic field detection sensor chip 23 is arranged in this closed magnetic path so that a magnetic field (bias magnetic field) is applied in a direction substantially perpendicular to the laminated surface.

The pair of permanent magnets 22b ₁ and 22b ₂ is formed of a rectangular parallelepiped ferrite material extending parallel to each other in the X-axis direction, and faces the second magnetic field detection sensor chip 24 for the X-axis and Z-axis. Yes. Permanent magnets 22b ₁ and 22b ₂ of these pair are surface facing the second magnetic field detection sensor 24 are arranged so that opposite polarities, to constitute a closed magnetic circuit in both. As will be described later, the spin valve GMR element of the second magnetic field detection sensor chip 24 is arranged in this closed magnetic path so that a bias magnetic field is applied in a direction substantially perpendicular to the laminated surface.

The pair of permanent magnets 22c ₁ and 22c ₂ is formed of a rectangular parallelepiped ferrite material extending in parallel with each other in the Y-axis direction, and faces the third magnetic field detection sensor chip 25 for the Y-axis. These pair of permanent magnets 22c ₁ and 22c ₂ is a surface facing the third magnetic field detection sensor 25 are arranged so that opposite polarities, to constitute a closed magnetic circuit in both. As will be described later, the spin valve GMR element of the third magnetic field detection sensor chip 25 is arranged in this closed magnetic path so that a bias magnetic field is applied in a direction substantially perpendicular to the laminated surface.

  FIG. 4 is a diagram schematically showing the connection on the wiring board and the configuration of the magnetic field detection sensor chip in the acceleration sensor of this embodiment, and FIG. 5 is an electrical diagram of the wiring board and the magnetic field detection sensor chip in the acceleration sensor of this embodiment. FIG. 6 is an equivalent circuit diagram of the acceleration sensor according to the present embodiment.

As shown in these drawings, the first magnetic field detection sensor chip 23 for detecting acceleration in the X-axis and Z-axis directions has a linear portion along a direction perpendicular to the X-axis direction (Y-axis direction). Four (two pairs) spin valve GMR elements 23a, 23b, 23c and 23d are formed in parallel to each other. The spin valve GMR elements 23a and 23b are paired and connected in series with each other. Both ends of the series connection are connected to the power supply terminal electrodes _TVCC and _TVDD , respectively, and the middle point is connected to the signal output terminal _TX1 . The spin valve GMR elements 23c and 23d are also paired and connected in series. Both ends of the series connection are connected to the power supply terminal electrodes _TVCC and _TVDD , respectively, and the middle point is connected to the signal output terminal _TZ1 .

  Each of the spin valve GMR elements 23a, 23b, 23c, and 23d basically includes a pinned layer made of an antiferromagnetic material and a pinned layer made of a ferromagnetic material, a nonmagnetic intermediate layer, and a ferromagnetic material. The pinned layer has a magnetization fixed in the same direction perpendicular to the extending direction of the free layer. That is, the pinned layers of the spin valve GMR elements 23a, 23b, 23c and 23d are all magnetization fixed in the same direction in the X-axis direction.

  FIG. 7 is a graph showing MR resistance change characteristics with respect to the applied magnetic field angle to the laminated surface of the spin valve GMR element. In the figure, the horizontal axis represents the angle (°) formed with the extending direction of the free layer of the applied magnetic field (direction perpendicular to the magnetization fixed direction), and the vertical axis represents the MR resistance (Ω). As can be seen from the figure, the MR resistance changes greatly even if the bias magnetic field changes slightly in the vicinity of 90 °. Since the change in the minute angle θ of the bias magnetic field is 90 ± θ, a slight inclination of the magnetic field generating weight member, and thus a pair of permanent magnets, is taken out as a resistance change, and not only the magnitude as a magnetization vector. The positive and negative directions can also be taken out.

The pinned layers of the paired spin valve GMR elements 23a and 23b connected in series with each other are fixed in magnetization in the same direction because the bias magnetic fields applied to each of the paired spin valve GMR elements are almost opposite to each other. Because there is. That is, as shown in FIG. 5, a closed magnetic path is constituted by a pair of permanent magnets 22a ₁ and 22a ₂ , and the paired spin valve GMR elements 23a and 23b have a magnetic path through which a reverse magnetic field of the closed magnetic path flows. This is because the bias magnetic fields are almost opposite to each other. The same applies to the paired spin valve GMR elements 23c and 23d connected in series. In this case, the center of the magnetic circuit constituting the closed magnetic circuit is located on the center line between the paired spin valve GMR elements.

  Thus, by applying bias magnetic fields in substantially opposite directions, the pinned layers of the spin valve GMR elements 23a and 23b and 23c and 23d forming a pair have the same magnetization fixed direction. Four spin valve GMR elements can be formed in one chip, and as a result, the entire acceleration sensor can be further reduced in size.

The second magnetic field detection sensor chip 24 for detecting acceleration in the X-axis and Z-axis directions also has four (two pairs) spins having straight portions along a direction perpendicular to the X-axis direction (Y-axis direction). Valve GMR elements 24a, 24b, 24c and 24d are formed in parallel to each other. The spin valve GMR elements 24b and 24a are paired and connected in series with each other. Both ends of the series connection are connected to the power supply terminal electrodes _TVCC and _TVDD , respectively, and the middle point is connected to the signal output terminal _TX2 . The spin valve GMR elements 24c and 24d are also paired and connected in series with each other. Both ends of the series connection are connected to the power supply terminal electrodes _TVCC and _TVDD , respectively, and the middle point is connected to the signal output terminal _TZ2 .

  Each of the spin valve GMR elements 24a, 24b, 24c, and 24d basically includes a pinned layer made of an antiferromagnetic material and a pinned layer made of a ferromagnetic material, a nonmagnetic intermediate layer, and a ferromagnetic material. The pinned layer has a magnetization fixed in the same direction perpendicular to the extending direction of the free layer. That is, the pinned layers of the spin valve GMR elements 24a, 24b, 24c and 24d are all magnetization fixed in the same direction in the X-axis direction.

The pinned layers of the paired spin valve GMR elements 24a and 24b connected in series with each other are fixed in magnetization in the same direction because the bias magnetic fields applied to each of the paired spin valve GMR elements are almost opposite to each other. Because there is. That is, as shown in FIG. 5, a closed magnetic path is constituted by a pair of permanent magnets 22b ₁ and 22b ₂ , and the paired spin valve GMR elements 24a and 24b have a magnetic path through which a reverse magnetic field of the closed magnetic path flows. This is because the bias magnetic fields are almost opposite to each other. The same applies to the paired spin valve GMR elements 24c and 24d connected in series. In this case, the center of the magnetic circuit constituting the closed magnetic circuit is located on the center line between the paired spin valve GMR elements.

  Thus, by applying bias magnetic fields in substantially opposite directions to each other, the pinned layers of the spin valve GMR elements 24a and 24b and 24c and 24d forming a pair have the same magnetization fixed direction. Four spin valve GMR elements can be formed in one chip, and as a result, the entire acceleration sensor can be further reduced in size.

The third magnetic field detection sensor chip 25 for detecting acceleration in the Y-axis direction includes four (two pairs) spin valves GMR having straight portions along a direction perpendicular to the Y-axis direction (X-axis direction). Elements 25a, 25b, 25c and 25d are formed in parallel to each other. The spin valve GMR elements 25a and 25b are paired and connected in series. Both ends of the series connection are connected to the power supply terminal electrodes _TVCC and _TVDD , respectively, and the middle point is connected to the signal output terminal _TY1 . The spin valve GMR elements 25c and 25d are also paired and connected in series with each other. Both ends of the series connection are connected to the power supply terminal electrodes _TVCC and _TVDD , respectively, and the middle point is connected to the signal output terminal _TY2 .

  Each of the spin valve GMR elements 25a, 25b, 25c and 25d basically includes a pinned layer made of an antiferromagnetic material and a pinned layer made of a ferromagnetic material, a nonmagnetic intermediate layer, and a ferromagnetic material. The pinned layer has a magnetization fixed in the same direction perpendicular to the extending direction of the free layer. That is, the pinned layers of these spin valve GMR elements 25a, 25b, 25c and 25d are all magnetization fixed in the same direction in the Y-axis direction.

The pinned layers of the paired spin valve GMR elements 25a and 25b connected in series with each other are fixed in magnetization in the same direction because the bias magnetic fields applied to each of the paired spin valve GMR elements are almost opposite to each other. Because there is. That is, as shown in FIG. 5, and a closed magnetic path is formed by the permanent magnets 22c ₁ and 22c ₂ of a pair, the spin valve GMR elements 25a and 25b as a pair, a magnetic path reverse magnetic field of the closed magnetic circuit flows This is because the bias magnetic fields are almost opposite to each other. The same applies to the paired spin valve GMR elements 25c and 25d connected in series. In this case, the center of the magnetic circuit constituting the closed magnetic circuit is located on the center line between the paired spin valve GMR elements.

  Thus, by applying bias magnetic fields in substantially opposite directions to each other, the pinned layers of the spin valve GMR elements 25a and 25b and 25c and 25d forming a pair have the same magnetization fixed direction. Four spin valve GMR elements can be formed in one chip, and as a result, the entire acceleration sensor can be further reduced in size.

A power supply voltage Vcc-Vdd is applied between the spin valve GMR elements 23a and 23b of the first magnetic field detection sensor chip 23, and a first X-axis direction acceleration signal V is _supplied from a signal output terminal T _X1 connected to the midpoint thereof. _X1 is taken out. Further, a power supply voltage Vcc-Vdd is applied between the spin valve GMR elements 24b and 24a of the second magnetic field detection sensor chip 24, and a second X-axis direction acceleration is applied from the signal output terminal T _X2 connected to the midpoint thereof. The signal V _X2 is taken out. Accordingly, the spin valve GMR elements 23a and 23b and the spin valve GMR elements 24b and 24a are connected in a full bridge as shown in FIG. 6A, and the signal output terminal T _X1 and the signal output terminal T _X2 are connected. The signals V _X1 and V _X2 are differentially amplified to become an acceleration signal in the X-axis direction. The acceleration signal in the X-axis direction is generated by the magnetic field generating weight member 22a (and hence the permanent magnets 22a ₁ and 22a ₂ ) and the magnetic field generating weight member 22b (and hence the permanent magnets 22b ₁ and 22b ₂ ) depending on the direction of the applied acceleration. This signal is output only when the Z axis is displaced in the opposite direction, and when both are displaced in the same direction, the first X axis direction acceleration signal V _X1 and the second X axis direction acceleration signal V _X2 cancel each other. Not output.

A power supply voltage Vcc-Vdd is applied between the spin valve GMR elements 23c and 23d of the first magnetic field detection sensor chip 23, and a first Z-axis direction acceleration signal V is supplied from a signal output terminal _TZ1 connected to the midpoint thereof. _Z1 is taken out. The power supply voltage Vcc-Vdd is applied between the spin valve GMR elements 24c and 24d of the second magnetic field detection sensor chip 24, and the second Z-axis direction acceleration is applied from the signal output terminal _TZ2 connected to the midpoint thereof. The signal _VZ2 is taken out. Therefore, these spin valve GMR elements 23c and 23d and the spin valve GMR elements 24c and 24d becomes a fact that connected in full-bridge configuration as shown in FIG. 6 (B), from the signal output terminal _{T Z1} and the signal output terminal _{T Z2} The signals V _Z1 and V _Z2 are differentially amplified to become an acceleration signal in the Z-axis direction. Acceleration signal in the Z-axis direction, the acceleration applied, the magnetic field generation members with weights 22a (hence the permanent magnets 22a ₁ and 22a ₂₎ and magnetic field generation members with weights 22b (hence the permanent magnets 22b ₁ and 22b ₂₎ and the Z-axis Are output only when they are displaced in the same direction, and when displaced in opposite directions, the first Z-axis direction acceleration signal V _Z1 and the second Z-axis direction acceleration signal V _Z2 cancel each other and are not output. .

A power supply voltage Vcc-Vdd is applied between the spin valve GMR elements 25b and 25a of the third magnetic field detection sensor chip 25, and a first Y-axis direction acceleration signal V is _supplied from a signal output terminal _TY1 connected to the midpoint thereof. _Y1 is extracted, the power supply voltage Vcc-Vdd is applied between the spin valve GMR elements 25c and 25d, and the second Y-axis direction acceleration signal _VY2 is extracted from the signal output terminal _TY2 connected to the midpoint thereof. . Therefore, the spin valve GMR elements 25a to 25d of the third magnetic field detection sensor chip 25 are connected in a full bridge as shown in FIG. 6C, and the signal output terminal _TY1 and the signal output terminal _TY2 The signals V _Y1 and V _Y2 are differentially amplified and become an acceleration signal in the Y-axis direction. Acceleration signal in the Y-axis direction, the acceleration applied, the magnetic field generation members with weights 22c (hence the permanent magnets 22c ₁ and 22c ₂₎ is output when displaced in the Z-axis direction.

  Next, the spring member 21 in the present embodiment will be described in more detail.

  FIG. 8 is a view for explaining the basic operation of the strip-shaped leaf spring in the spring member of the present invention.

  FIG. 6A shows a case where no external force is applied, 80 is a belt-like leaf spring, 81 is a bending center or fulcrum located at one end thereof, and 82 is a position displaced from the bending center 81. The weight members fixed to one surface of the other end of the leaf spring 80 are shown. For the following explanation, a direction perpendicular to the surface of the strip-shaped leaf spring 80 is defined as a bending direction, and a longitudinal direction of the strip-shaped leaf spring 80 is defined as a length direction.

  The strip leaf spring 80 is subjected to bending stress both when an external force is applied in the bending direction as shown in FIG. 5B and when an external force is applied in the length direction as shown in FIG. The end portion and the weight member 82 are displaced in the bending direction.

  FIG. 9 is a belt spring having a configuration in which the belt spring shown in FIG. 8 is developed on both sides from the bending center, in other words, it has a fulcrum 91 at the center and weight members 92a and 92b are attached to both ends. It is a figure explaining operation | movement of the obtained strip | belt-shaped leaf | plate spring 90. FIG.

  FIG. 6A shows a case where an external force Fz is applied in the bending direction. In this case, both ends of the belt-like plate spring 90 and the weight members 92a and 92b are displaced in the same bending direction. On the other hand, FIG. 5B shows a case where an external force Fx is applied in the length direction. In this case, both end portions of the belt-like plate spring 90 and the weight members 92a and 92b are displaced in opposite bending directions. Here, when the external force Fz in FIG. 10A and the external force Fx in FIG. 10B are | Fz | = | Fx |, the displacement amounts of the weight members 92a and 92b are equal. The amount of displacement of the weight members 92a and 92b is proportional to the displacement angle θ of the weight members 92a and 92b. If the weight member is a permanent magnet that generates a magnetic field, the spin valve GMR element can detect the applied external force by detecting the displacement angle θ.

  FIG. 10 is a view for explaining the operation of the spring member in the present embodiment. However, in FIG. 10, the extension directions of the magnetic field generating weight members 22c and 22d are shown differently from the present embodiment, but the operation as a spring member is the same.

  As shown in FIG. 6A, when an external force Fx in the X-axis direction is applied, the first belt-like leaf spring 21a that is the main spring and the second belt-like leaf springs 21b and 21c that are the secondary springs are both bent. Stress is generated and displaced in the bending direction of the main spring to a position where equilibrium is maintained. In this case, the displacement directions of the magnetic field generating weight members 22a and 22c and the magnetic field generating weight members 22b and 22d are opposite to each other. As shown in FIG. 5B, when an external force Fz in the Z-axis direction is applied, the first belt-like leaf spring 21a that is the main spring and the second belt-like leaf springs 21b and 21c that are the auxiliary springs are both bent. Stress is generated and displaced in the bending direction of the main spring to a position where equilibrium is maintained. However, in this case, the displacement directions of the magnetic field generating weight members 22a and 22c and the magnetic field generating weight members 22b and 22d are the same. Furthermore, as shown in FIG. 6C, when an external force Fy in the Y-axis direction is applied, the first strip-shaped leaf spring 21a, which is the main spring, exhibits a torsional stress that rotates about the center in the length direction. The second belt springs 21b and 21c, which are auxiliary springs, generate bending stress and are displaced in the rotational direction about the center in the longitudinal direction of the main spring to a position where equilibrium is maintained. In this case, the displacement directions of the magnetic field generating weight members 22a and 22b and the magnetic field generating weight members 22c and 22d are opposite to each other.

When an external force Fx in the X-axis direction is applied and the magnetic field generating weight members 22a and 22c and the magnetic field generating weight members 22b and 22d are displaced in the bending direction of the main spring as described above, the spin valve GMR elements 23a and 23b and 24b and 24a are applied. Accordingly, the angle of the applied bias magnetic field changes in the same direction, and a differential output obtained by adding the first X-axis direction acceleration signal V _X1 and the second X-axis direction acceleration signal V _X2 is obtained. It becomes an acceleration signal in the X-axis direction. In this case, the first Z-axis direction acceleration signal V _Z1 and the second Z-axis direction acceleration signal V _Z2 cancel each other, and no Z-axis direction acceleration signal is output. In this case, since the angle of the bias magnetic field changes along the extending direction of the free layer of the spin valve GMR elements 25d, 25b, 25c, and 25a, the first Y-axis direction acceleration signal V _Y1 and the second Y The axial direction acceleration signal V _Y2 is not output, and therefore the Y axis direction acceleration signal is not output.

When an external force Fz in the Z-axis direction is applied and the magnetic field generating weight members 22a and 22c and the magnetic field generating weight members 22b and 22d are displaced in the bending direction of the main spring as described above, they are applied to the spin valve GMR elements 23c and 23d and 24c and 24d. Accordingly, the angle of the applied bias magnetic field changes in the opposite direction, and a differential output obtained by adding the first Z-axis direction acceleration signal V _Z1 and the second Z-axis direction acceleration signal V _Z2 is obtained. It becomes an acceleration signal in the Z-axis direction. In this case, the first X-axis direction acceleration signal V _X1 and the second X-axis direction acceleration signal V _X2 cancel each other, and no X-axis direction acceleration signal is output. In this case, since the angle of the bias magnetic field changes along the extending direction of the free layer of the spin valve GMR elements 25d, 25b, 25c, and 25a, the first Y-axis direction acceleration signal V _Y1 and the second Y The axial direction acceleration signal V _Y2 is not output, and therefore the Y axis direction acceleration signal is not output.

When an external force Fy in the Y-axis direction is applied and the magnetic field generating weight members 22a and 22c and the magnetic field generating weight members 22b and 22d are displaced in the rotational direction with the center in the length direction of the main spring as described above, the spin valve GMR The angle of the bias magnetic field applied to the elements 25d, 25b, 25c and 25a changes in the same direction accordingly, and the first Y-axis direction acceleration signal _VY1 and the second Y-axis direction acceleration signal _VY2 are added. A differential output is obtained, which becomes an acceleration signal in the Y-axis direction. In this case, since the angle of the bias magnetic field changes along the extending direction of the free layers of the spin valve GMR elements 23a to 23d and 24a to 24d, the first X-axis direction acceleration signal V _X1 and the second X The axial acceleration signal V _X2 , the first Z-axis direction acceleration signal V _Z1, and the second Z-axis direction acceleration signal V _Z2 are not output, and accordingly, the X-axis direction and Z-axis direction acceleration signals are not output.

  As described above, according to the present embodiment, the first belt-like leaf spring 21a that is the main spring and the second belt-like leaf springs 21b and 21c that are the secondary springs both generate bending stress and maintain the equilibrium. Therefore, the spring structure is small and has a large amount of displacement. Therefore, the spring structure can be small and highly sensitive, and a small and highly sensitive acceleration sensor can be provided.

  Since the structure of the four end portions of the spring member can have the same shape, an acceleration sensor having the sensitivity and sensitivity directivity in each direction (X-axis direction, Y-axis direction, Z-axis direction) to be detected is provided. be able to.

Furthermore, according to the present embodiment, the bending operation of the first strip-shaped leaf spring 21a having a fulcrum at the center and the magnetic field generating weight members fixed to both ends is used, and one of the first magnetic field detection sensor chips 23 is used. Since the differential output between the partial output V _X1 or V _Z1 and the partial output V _X2 or V _{Z2 of} the second magnetic field detection sensor chip 24 is taken out, the acceleration component in the X-axis direction and the Z-axis direction is surely obtained. Can be detected accurately. In addition, while utilizing the torsional motion of the first strip leaf spring 21a and devising the magnetic field detection direction of the third magnetic field detection sensor chip 25, the acceleration component in the Y-axis direction is reliably separated and accurately Can be detected.

  In addition, since the direction and magnitude of acceleration in the X-axis direction, Y-axis direction, and Z-axis direction can be detected by three magnetic field detection sensor chips, the number of magnetic field detection sensor chips can be reduced, and the structure can be greatly simplified. The whole can be reduced in size. In addition, since the spin valve GMR element has a very high magnetic detection sensitivity, it is possible to detect acceleration with high sensitivity.

  Further, in each magnetic field detection sensor chip, bias magnetic fields in opposite directions are applied to each other, so that the pinned layer magnetization direction of the paired spin valve GMR elements becomes the same direction, and the four spin valve GMR elements forming these pairs Can be formed in one chip. As a result, the entire acceleration sensor can be further reduced in size.

  Furthermore, according to the present embodiment, a closed magnetic circuit is formed by a vertical magnetic field distributed over a wide range by two permanent magnets in a pair, and the spin valve GMR element is disposed in this closed magnetic circuit. Only the minimum necessary magnetic field leaks from the closed magnetic path to the outside, and since the leakage magnetic field is reduced, a sufficiently large bias magnetic field is applied. Even when the permanent magnet is downsized, the detection sensitivity of acceleration is stable. However, it is difficult to be affected by an external electric field and an external magnetic field.

  Further, according to the present embodiment, since it is not necessary to provide an electrode on the spring member or the magnetic field generating weight member, the wiring structure is simplified. Further, since it has a lower impedance than a piezoelectric element type acceleration sensor or a capacitance type acceleration sensor, it is not easily affected by disturbances.

  FIG. 11 is a perspective view schematically showing the configuration of a spring member and a magnetic field generating weight member in another embodiment of the acceleration sensor of the present invention. The configuration excluding the spring member and the magnetic field generating weight member in this embodiment is the same as that in the embodiment of FIG. Accordingly, in FIG. 11, the same reference numerals are used for the same components as in the embodiment of FIG.

  The structure of the spring member in the present embodiment is the same as that in the embodiment of FIG. The difference is that the magnetic field generating weight members 22a to 22d are on the surface on the magnetic field detection sensor chip side of the weight support portions provided at both ends of the second belt springs 21b and 21c, that is, the embodiment of FIG. It is in the point fixed on the surface on the opposite side. The four magnetic field generating weight members may be attached to either side of the spring member.

  Other configurations of the spring member and the magnetic field generating weight member of the present embodiment, and the operation, effects, and the like of the present embodiment are the same as those of the embodiment of FIG.

  FIG. 12 is a perspective view schematically showing a configuration of a spring member and a magnetic field generating weight member in still another embodiment of the acceleration sensor of the present invention. The configuration excluding the spring member and the magnetic field generating weight member in this embodiment is the same as that in the embodiment of FIG. Accordingly, in FIG. 12, the same reference numerals are used for the same components as in the embodiment of FIG.

  The structure of the spring member in the present embodiment is the same as that in the embodiment of FIG. The difference is that the magnetic field generating weight members 22a, 22b, 22c ′ and 22d ′ are on the surface of the weight supporting portion provided at both ends of the second strip-shaped leaf springs 21b and 21c on the magnetic field detection sensor chip side, That is, they are fixed on the surface opposite to the embodiment of FIG. 2 and the extension directions of the magnetic field generating weight members 22c ′ and 22d ′ are different. The four magnetic field generating weight members may be attached to either side of the spring member. Further, the four magnetic field generating weight members respectively provided at both end portions of the second strip-shaped plate springs 21b and 21c may be balanced in weight even if they have different directions and shapes.

  Other configurations of the spring member and the magnetic field generating weight member of the present embodiment, and the operation, effects, and the like of the present embodiment are the same as those of the embodiment of FIG.

  FIG. 13 is a perspective view schematically showing a configuration of a spring member and a magnetic field generating weight member in still another embodiment of the acceleration sensor of the present invention. The configuration excluding the spring member and the magnetic field generating weight member in this embodiment is the same as that in the embodiment of FIG. Accordingly, in FIG. 13, the same reference numerals are used for the same components as in the embodiment of FIG.

  The structure of the spring member in the present embodiment is the same as that in the embodiment of FIG. The difference is that the magnetic field generating weight members 22a to 22d are on the surface on the magnetic field detection sensor chip side of the weight support portions provided at both ends of the second belt springs 21b and 21c, that is, the embodiment of FIG. And the points where the magnetic field generating weight members 22a and 22c and the magnetic field generating weight members 22b and 22d are connected by the rigid belt-like support members 130a and 130b, respectively. It is in. The four magnetic field generating weight members may be attached to either side of the spring member. Since the belt-like support members 130a and 130b are fixed, the second belt-like leaf springs 21b and 21c do not spring, and only the first belt-like leaf spring 21a springs. The first belt spring 21a generates bending stress and torsional stress against the force applied from the outside, and displaces the magnetic field generating weight members 22a to 22d.

  Other configurations of the spring member and the magnetic field generating weight member of the present embodiment, and the operation, effects, and the like of the present embodiment are the same as those of the embodiment of FIG.

  FIG. 14 is a perspective view schematically showing a configuration of a spring member and a magnetic field generating weight member in still another embodiment of the acceleration sensor of the present invention. The configuration excluding the spring member and the magnetic field generating weight member in this embodiment is the same as that in the embodiment of FIG. Accordingly, in FIG. 14, the same reference numerals are used for the same components as in the embodiment of FIG.

  The structure of the spring member in the present embodiment is the same as that in the embodiment of FIG. The difference is that the extension directions of the magnetic field generating weight members 22c ′ and 22d ′ are different from each other, and the magnetic field generating weight members 22a and 22c ′ and the magnetic field generating weight members 22b and 22d ′ are rigid band-shaped support members 130a. And 130b, respectively. The four magnetic field generating weight members respectively provided at both end portions of the second strip-shaped plate springs 21b and 21c may be balanced in weight even if they have different directions and shapes. Since the belt-like support members 130a and 130b are fixed, the second belt-like leaf springs 21b and 21c do not spring, and only the first belt-like leaf spring 21a springs. The first strip leaf spring 21a generates bending stress and torsional stress against the force applied from the outside, and displaces the magnetic field generating weight members 22a, 22b, 22c 'and 22d'.

  Other configurations of the spring member and the magnetic field generating weight member of the present embodiment, and the operation, effects, and the like of the present embodiment are the same as those of the embodiment of FIG.

  FIG. 15 is a perspective view schematically showing a configuration of a spring member and a magnetic field generating weight member in still another embodiment of the acceleration sensor of the present invention. The configuration excluding the spring member and the magnetic field generating weight member in this embodiment is the same as that in the embodiment of FIG. Accordingly, in FIG. 15, the same reference numerals are used for the same components as in the embodiment of FIG.

  The structure of the spring member in the present embodiment is the same as that in the embodiment of FIG. The difference is that the extension directions of the magnetic field generating weight members 22c ′ and 22d ′ are different, and the rigid belt-like support members 130a and 130b are fixed on the second belt-like leaf springs 21b and 21c. Further, a magnetic field generating weight member is fixed thereon, and the magnetic field generating weight members 22a and 22c ′ and the magnetic field generating weight members 22b and 22d ′ are connected by the belt-like support members 130a and 130b, respectively. The four magnetic field generating weight members respectively provided at both end portions of the second strip-shaped plate springs 21b and 21c may be balanced in weight even if they have different directions and shapes. If the weight balance is not lost, the belt-like support members 130a and 130b may be provided at any position on the top, bottom, left and right of the magnetic field generating weight member. Since the belt-like support members 130a and 130b are fixed, the second belt-like leaf springs 21b and 21c do not spring, and only the first belt-like leaf spring 21a springs. The first strip leaf spring 21a generates bending stress and torsional stress against the force applied from the outside, and displaces the magnetic field generating weight members 22a, 22b, 22c 'and 22d'.

  Other configurations of the spring member and the magnetic field generating weight member of the present embodiment, and the operation, effects, and the like of the present embodiment are the same as those of the embodiment of FIG.

  FIG. 16 is a perspective view schematically showing a configuration of a spring member and a magnetic field generating weight member in still another embodiment of the acceleration sensor of the present invention. The configuration excluding the spring member and the magnetic field generating weight member in this embodiment is the same as that in the embodiment of FIG. Accordingly, in FIG. 16, the same reference numerals are used for the same components as in the embodiment of FIG.

  The structure of the spring member in the present embodiment is the same as that in the embodiment of FIG. The difference is that the magnetic field generating weight member is composed of two magnetic field generating weight members 162a and 162b, and these magnetic field generating weight members 162a and 162b are integrally fixed to the second belt springs 21b and 21c, respectively. It is in the point. Since the magnetic field generating weight members 162a and 162b are fixed integrally, the second strip-shaped plate springs 21b and 21c do not perform the spring operation, and only the first strip-shaped plate spring 21a performs the spring operation. The first belt spring 21a generates a bending stress and a torsional stress in response to an externally applied force, and displaces the magnetic field generating weight members 162a and 162b. Each of the magnetic field generating weight members 162a and 162b includes four pairs of permanent magnets as shown in the embodiment of FIG. 2 and weight members incorporating these permanent magnets.

  Other configurations of the spring member and the magnetic field generating weight member of the present embodiment, and the operation, effects, and the like of the present embodiment are the same as those of the embodiment of FIG.

  FIG. 17 is a perspective view schematically showing a configuration of a spring member and a magnetic field generating weight member in still another embodiment of the acceleration sensor of the present invention. The configuration excluding the spring member, the magnetic field generating weight member, and the fulcrum member in this embodiment is the same as that in the embodiment of FIG. Accordingly, in FIG. 17, the same reference numerals are used for the same components as in the embodiment of FIG.

In the present embodiment, the first strip-shaped leaf spring that constitutes the main spring and generates bending stress and / or torsional stress with respect to externally applied force is divided into two. and a strip-shaped plate spring 171a ₁ and 171a _2. Further, one end of the first strip-shaped plate springs 171a ₁ and 171a ₂ constitutes a fulcrum, and this one end is fixed to the other end of the fulcrum members 176a and 176b whose one end is fixed to the wiring board. The central portions of the two second belt springs 171b and 171c that constitute the secondary spring and generate only a bending stress with respect to the force applied from the outside are the first belt springs 171a ₁ and 171a ₂ . The other end is integrally connected to each other. Magnetic field generating weight members 22a, 22b, 22c 'and 22d' are fixed to both ends of the second strip-shaped plate springs 171b and 171c. Further, in the present embodiment, the magnetic field generating weight members 22a, 22b, 22c 'and 22d' are on the surface of the weight support portion provided on both ends of the second strip-shaped plate springs 21b and 21c on the magnetic field detection sensor chip side. In other words, the magnetic field generating weight members 22c 'and 22d' are different from each other in the extension direction of the embodiment shown in FIG. Even if the main spring is divided into two as in the spring member of this embodiment, the same function as in the embodiment of FIG. 2 can be obtained. Further, the four magnetic field generating weight members may be attached to either side of the spring member. Further, the four magnetic field generating weight members respectively provided at both ends of the second strip-shaped plate springs 171b and 171c may be balanced in weight even if they have different directions and shapes.

  Other configurations of the spring member and the magnetic field generating weight member of the present embodiment, and the operation, effects, and the like of the present embodiment are the same as those of the embodiment of FIG.

  FIG. 18 is a perspective view schematically showing a configuration of a spring member and a magnetic field generating weight member in still another embodiment of the acceleration sensor of the present invention. The configuration excluding the spring member, the magnetic field generating weight member, and the fulcrum member in this embodiment is the same as that in the embodiment of FIG. Accordingly, in FIG. 18, the same reference numerals are used for the same components as in the embodiment of FIG.

In the present embodiment, the first strip-shaped leaf spring that constitutes the main spring and generates bending stress and / or torsional stress with respect to externally applied force is divided into two. and a strip-shaped plate spring 171a ₁ and 171a _2. Further, one end of the first strip-shaped plate springs 171a ₁ and 171a ₂ constitutes a fulcrum, and this one end is fixed to the other end of the fulcrum members 176a and 176b whose one end is fixed to the wiring board. The central portions of the two second belt springs 171b and 171c that constitute the secondary spring and generate only a bending stress with respect to the force applied from the outside are the first belt springs 171a ₁ and 171a ₂ . The other end is integrally connected to each other. Magnetic field generating weight members 22a, 22b, 22c 'and 22d' are fixed to both ends of the second strip-shaped plate springs 171b and 171c. Further, in the present embodiment, the magnetic field generating weight members 22a and 22c ′ and the magnetic field generating weight members 22b and 22d ′ are connected by the belt-shaped support members 180a and 180b having rigidity, respectively, and the magnetic field generating weight members 22c ′ and 22d are connected. The extension direction of ′ is different from that in the embodiment of FIG. Even if the main spring is divided into two as in the spring member of this embodiment, the same function as in the embodiment of FIG. 2 can be obtained. Further, since the belt-like support members 180a and 180b are fixed, the second belt-like plate springs 171b and 171c do not operate as springs, and only the first belt-like plate springs 171a ₁ and 171a ₂ operate as springs. . The first belt springs 171a ₁ and 171a ₂ generate bending stress and torsional stress against the force applied from the outside, and displace the magnetic field generating weight members 22a, 22b, 22c 'and 22d'. Further, the four magnetic field generating weight members respectively provided at both ends of the second strip-shaped plate springs 171b and 171c may be balanced in weight even if they have different directions and shapes.

  Other configurations of the spring member and the magnetic field generating weight member of the present embodiment, and the operation, effects, and the like of the present embodiment are the same as those of the embodiment of FIG.

  FIG. 19 is an exploded perspective view schematically showing an overall configuration of still another embodiment of the acceleration sensor of the present invention, and FIG. 20 is a spring member provided inside the housing member, a magnetic field generating weight member, and a magnetic field detection sensor. It is a disassembled perspective view which shows the structure of a chip | tip schematically.

  As shown in these drawings, the acceleration sensor in the present embodiment is for detecting biaxial acceleration in the X-axis direction and the Z-axis direction or the Y-axis direction and the Z-axis direction. However, in the following description, it is assumed to detect biaxial acceleration in the X-axis direction and the Z-axis direction.

  This acceleration sensor includes a spring member 191 formed integrally with a belt spring 191a and two weight support portions 191b and 191c for supporting a magnetic field generating weight member in a housing member 190, and a size and shape. And two magnetic field generation weight members 192a and 192b having the same configuration such as weight, the first magnetic field detection sensor chip 193 for the X axis and Z axis, and the second magnetic field detection sensor chip 194 for the X axis and Z axis. And the fulcrum member 196 are housed.

  The housing member 190 includes a wiring board 190a formed by providing a wiring pattern (not shown) on a flat board made of a resin material such as polyimide or BT resin, and covers and seals the wiring board 190a. The cover member 190b is made of a magnetic metal material. In the present embodiment, the two-axis acceleration in the X-axis direction and the Z-axis direction can be detected by the two magnetic field detection sensor chips 193 and 194 mounted on one plane by the wiring board 190a.

  In this embodiment, the spring member 21 is integrally formed by processing a thin metal plate such as NiFe or Ni, a thin plate such as stainless steel, or a thin resin plate such as polyimide in this embodiment as shown in FIG. Is formed.

  The strip-shaped leaf spring 191a generates a bending stress with respect to an externally applied force. The central portion of the strip-shaped plate spring 191a constitutes a fulcrum, and this central portion is fixed to the other end of the fulcrum member 196 whose one end is fixed to the cover member 190b. Both ends of the belt-like plate spring 191a are integrally connected to weight support portions 191b and 191c having the same shape. The weight support portions 191b and 191c are rectangular in the drawing, but may be circular or other shapes.

The magnetic field generating weight members 192a and 192b are fixed to one surface of the weight support portions 191b and 191c of the spring member 191 with an adhesive, respectively. Magnetic field generation members with weights 192a and 192b, respectively, and a permanent magnet 192a ₁ and 192a ₂ and 192b ₁ and 192b ₂ of the pair of magnetic field generating.

  The first magnetic field detection sensor chip 193 and the second magnetic field detection sensor chip 194 for the X axis and the Z axis are fixed to the wiring board 190a with an adhesive so as to face the two magnetic field generation weight members 192a and 192b, respectively. ing. Therefore, the magnetic field generating weight members 192a and 192b apply a magnetic field whose angle changes according to the acceleration to the first and second magnetic field detection sensor chips 193 and 194, respectively.

The pair of permanent magnets 192a ₁ and 192a ₂ are formed of a rectangular parallelepiped ferrite material extending in parallel with each other in the X-axis direction, and face the first magnetic field detection sensor chip 193 for the X-axis and Z-axis. Yes. The pair of permanent magnets 192a ₁ and 192a ₂ are arranged so that the surfaces facing the first magnetic field detection sensor chip 193 have opposite polarities, and both form a closed magnetic circuit. As will be described later, the spin valve GMR element of the first magnetic field detection sensor chip 193 is arranged in this closed magnetic path so that a magnetic field (bias magnetic field) is applied in a direction substantially perpendicular to the laminated surface.

The pair of permanent magnets 192b ₁ and 192b ₂ are formed of a rectangular parallelepiped ferrite material extending parallel to each other in the X-axis direction, and face the second magnetic field detection sensor chip 194 for the X-axis and Z-axis. Yes. The pair of permanent magnets 192b ₁ and 192b ₂ are disposed so that the surfaces facing the second magnetic field detection sensor chip 194 have opposite polarities, and both form a closed magnetic circuit. As will be described later, the spin valve GMR element of the second magnetic field detection sensor chip 194 is arranged in this closed magnetic path so that a bias magnetic field is applied in a direction substantially perpendicular to the laminated surface.

  FIG. 21 is a diagram schematically showing the connection on the wiring board and the configuration of the magnetic field detection sensor chip in the acceleration sensor of the present embodiment, and FIG. 22 is an electrical diagram of the wiring board and magnetic field detection sensor chip in the acceleration sensor of the present embodiment. FIG. 23 is an equivalent circuit diagram of the acceleration sensor of the present embodiment.

As shown in these drawings, the first magnetic field detection sensor chip 193 for detecting acceleration in the X-axis and Z-axis directions has a straight line portion along a direction perpendicular to the X-axis direction (Y-axis direction). Four (two pairs) spin valve GMR elements 193a, 193b, 193c and 193d are formed in parallel to each other. The spin valve GMR elements 193a and 193b are paired and connected in series with each other. Both ends of the series connection are connected to the power supply terminal electrodes _TVCC and _TVDD , respectively, and the middle point is connected to the signal output terminal _TX1 . The spin valve GMR elements 193c and 193d are also paired and connected in series with each other. Both ends of the series connection are connected to the power supply terminal electrodes _TVCC and _TVDD , respectively, and the middle point is connected to the signal output terminal _TZ1 .

  Each of the spin valve GMR elements 193a, 193b, 193c, and 193d basically includes a pinned layer made of an antiferromagnetic material and a pinned layer made of a ferromagnetic material, a nonmagnetic intermediate layer, and a ferromagnetic material. The pinned layer has a magnetization fixed in the same direction perpendicular to the extending direction of the free layer. That is, the pinned layers of the spin valve GMR elements 193a, 193b, 193c, and 193d are all magnetization fixed in the same direction in the X-axis direction.

The pinned layers of the pair of spin valve GMR elements 193a and 193b connected in series with each other are magnetization fixed in the same direction because the bias magnetic fields applied to each of the paired spin valve GMR elements are almost opposite to each other. Because there is. That is, as shown in FIG. 22, a pair of permanent magnets 192a ₁ and 192a ₂ form a closed magnetic circuit, and the paired spin valve GMR elements 193a and 193b have a magnetic path through which a reverse magnetic field of the closed magnetic circuit flows. This is because the bias magnetic fields are almost opposite to each other. The same applies to the paired spin valve GMR elements 193c and 193d connected in series. In this case, the center of the magnetic circuit constituting the closed magnetic circuit is located on the center line between the paired spin valve GMR elements.

  Thus, by applying bias magnetic fields in substantially opposite directions, the pinned layers of the spin valve GMR elements 193a and 193b and 193c and 193d forming a pair have the same magnetization fixed direction. Four spin valve GMR elements can be formed in one chip, and as a result, the entire acceleration sensor can be further reduced in size.

The second magnetic field detection sensor chip 194 for detecting acceleration in the X-axis and Z-axis directions also has four (two pairs) spins having straight portions along the direction perpendicular to the X-axis direction (Y-axis direction). Valve GMR elements 194a, 194b, 194c and 194d are formed in parallel to each other. The spin valve GMR elements 194b and 194a are paired and connected in series with each other. Both ends of the series connection are connected to the power supply terminal electrodes _TVCC and _TVDD , respectively, and the middle point is connected to the signal output terminal _TX2 . The spin valve GMR elements 194c and 194d are also paired and connected in series with each other. Both ends of the series connection are connected to the power supply terminal electrodes _TVCC and _TVDD , respectively, and the middle point is connected to the signal output terminal _TZ2 .

  Each of the spin valve GMR elements 194a, 194b, 194c and 194d basically includes a pinned layer made of an antiferromagnetic material and a pinned layer made of a ferromagnetic material, a nonmagnetic intermediate layer, and a ferromagnetic material. The pinned layer has a magnetization fixed in the same direction perpendicular to the extending direction of the free layer. That is, the pinned layers of these spin valve GMR elements 194a, 194b, 194c and 194d are all magnetization fixed in the same direction in the X-axis direction.

The pinned layers of the paired spin valve GMR elements 194a and 194b connected in series with each other are fixed in magnetization in the same direction because the bias magnetic fields applied to each of the paired spin valve GMR elements are almost opposite to each other. Because there is. That is, as shown in FIG. 22, a pair of permanent magnets 192b ₁ and 192b ₂ form a closed magnetic path, and the paired spin valve GMR elements 194a and 194b have a magnetic path through which a reverse magnetic field flows. This is because the bias magnetic fields are almost opposite to each other. The same applies to the pair of spin valve GMR elements 194c and 194d connected in series. In this case, the center of the magnetic circuit constituting the closed magnetic circuit is located on the center line between the paired spin valve GMR elements.

  Thus, by applying bias magnetic fields in substantially opposite directions, the pinned layers of the spin valve GMR elements 194a and 194b and 194c and 194d forming a pair have the same magnetization fixed direction. Four spin valve GMR elements can be formed in one chip, and as a result, the entire acceleration sensor can be further reduced in size.

A power supply voltage Vcc-Vdd is applied between the spin valve GMR elements 193a and 193b of the first magnetic field detection sensor chip 193, and a first X-axis direction acceleration signal V is applied from a signal output terminal T _X1 connected to the midpoint thereof. _X1 is taken out. Further, between the second magnetic field spin valve GMR elements 194b of the detection sensor 194 and 194a supply voltage Vcc-Vdd is applied, a second X-axis direction acceleration from the signal output terminal _{T X2} that is connected to the midpoint The signal V _X2 is taken out. Therefore, the spin valve GMR elements 193a and 193b and 194b and 194a are connected in a full bridge as shown in FIG. 23A, and the signal V _X1 from the signal output terminal T _X1 and the signal output terminal T _{X2 is obtained.} And V _X2 are differentially amplified to become an acceleration signal in the X-axis direction. Acceleration signal in the X-axis direction, the direction of the applied acceleration, magnetic field generation members with weights 192a (hence the permanent magnets 192a ₁ and 192a ₂₎ and magnetic field generation members with weights 192b (hence the permanent magnet 192b ₁ and 192b ₂₎ and is This signal is output only when the Z axis is displaced in the opposite direction, and when both are displaced in the same direction, the first X axis direction acceleration signal V _X1 and the second X axis direction acceleration signal V _X2 cancel each other. Not output.

The first power supply voltage Vcc-Vdd is applied across the spin valve GMR elements 193c and 193d of the magnetic field detection sensor 193, a first Z-axis acceleration signal V from the signal output terminal _{T Z1} connected to the midpoint _Z1 is taken out. Further, between the second magnetic field spin valve GMR elements 194c of the detection sensor 194 and 194d supply voltage Vcc-Vdd is applied, a second Z-axis direction acceleration from the signal output terminal _{T Z2} which is connected to the midpoint The signal _VZ2 is taken out. Therefore, the spin valve GMR elements 193c and 193d and 194c and 194d are connected in a full bridge as shown in FIG. 23B, and the signal V _Z1 from the signal output terminal T _Z1 and the signal output terminal T _{Z2 is shown.} And V _Z2 are differentially amplified to become an acceleration signal in the Z-axis direction. The acceleration signal in the Z-axis direction is such that the magnetic field generating weight member 192a (and hence the permanent magnets 192a ₁ and 192a ₂ ) and the magnetic field generating weight member 192b (and hence the permanent magnets 192b ₁ and 192b ₂ ) are Z-axis depending on the applied acceleration. Are output only when they are displaced in the same direction, and when displaced in opposite directions, the first Z-axis direction acceleration signal V _Z1 and the second Z-axis direction acceleration signal V _Z2 cancel each other and are not output. .

  Next, the spring member 191 in this embodiment will be described in more detail.

  FIG. 24 is a view for explaining the operation of the spring member in the present embodiment.

FIG. 6A shows a case where no external force is applied, and no displacement occurs. On the other hand, when an external force Fx is applied in the X-axis direction as shown in FIG. 5B, the strip-shaped leaf spring 191a generates bending stress and is displaced in the bending direction to a position where equilibrium is maintained. In this case, the displacement directions of both end portions of the strip-shaped plate spring 191a and the magnetic field generating weight members 192a and 192b are opposite to each other. When an external force Fz is applied in the Z-axis direction as shown in FIG. 3C, the strip-shaped plate spring 191a generates bending stress and is displaced in the bending direction to a position where equilibrium is maintained. In this case, both ends of the strip-shaped plate spring 191a and the displacement directions of the magnetic field generating weight members 192a and 192b are the same direction. The displacement amounts of the magnetic field generating weight members 192a and 192b are proportional to their displacement angles. When the angle of the magnetic field generating weight member changes in this way, the spin valve GMR element can detect the applied external force by detecting the displacement angle. When the displacement angles of the magnetic field generating weight members 192a and 192b when the external force Fx is applied are θ _X1 and θ _X2 , respectively, Fx = θ _X1 −θ _X2 is given. Further, if the displacement angles of the magnetic field generating weight members 192a and 192b when the external force Fz is applied are θ _Z1 and θ _Z2 , respectively, Fz = θ _Z1 + θ _Z2 is given.

When the external force Fx in the X-axis direction is applied and the magnetic field generating weight members 192a and 192b are displaced in the bending direction as described above, the angle of the bias magnetic field applied to the spin valve GMR elements 193a and 193b and 194b and 194a is accompanied by this. Thus, a differential output obtained by adding the first X-axis direction acceleration signal V _X1 and the second X-axis direction acceleration signal V _X2 is obtained, and this becomes an X-axis direction acceleration signal. In this case, the first Z-axis direction acceleration signal V _Z1 and the second Z-axis direction acceleration signal V _Z2 cancel each other, and no Z-axis direction acceleration signal is output.

When the external force Fz in the Z-axis direction is applied and the magnetic field generating weight members 192a and 192b are displaced in the bending direction as described above, the angle of the bias magnetic field applied to the spin valve GMR elements 193c and 193d and 194c and 194d is accompanied by this. Thus, a differential output obtained by adding the first Z-axis direction acceleration signal V _Z1 and the second Z-axis direction acceleration signal V _Z2 is obtained, and this becomes an acceleration signal in the Z-axis direction. In this case, the first X-axis direction acceleration signal V _X1 and the second X-axis direction acceleration signal V _X2 cancel each other, and no X-axis direction acceleration signal is output.

  As described above, according to the present embodiment, the strip-shaped plate spring 191a is configured to be displaced to a position where the bending stress is generated and the equilibrium is maintained, so that it is small and has a large displacement. A small and highly sensitive spring structure can be provided, and a small and highly sensitive acceleration sensor can be provided.

  Since the two ends of the spring member can have the same shape, the sensitivity and sensitivity directivity in each direction (X-axis direction and Z-axis direction, or Y-axis direction and Z-axis direction) to be detected are aligned. An acceleration sensor can be provided.

Further, according to the present embodiment, the bending operation of the strip-shaped plate spring 191a having a fulcrum at the center and the magnetic field generating weight members fixed to both ends is used, and a partial output of the first magnetic field detection sensor chip 193 is used. Since the differential output between V _X1 or V _Z1 and the partial output V _X2 or V _{Z2 of} the second magnetic field detection sensor chip 194 is taken out, the acceleration components in the X-axis direction and the Z-axis direction are reliably separated. And can be detected accurately.

  In addition, since the direction and magnitude of the acceleration in the biaxial direction can be detected by two magnetic field detection sensor chips, the number of magnetic field detection sensor chips can be reduced, the structure can be greatly simplified, and the entire acceleration sensor can be reduced in size. . In addition, since the spin valve GMR element has a very high magnetic detection sensitivity, it is possible to detect acceleration with high sensitivity.

  Furthermore, in each magnetic field detection sensor chip, bias magnetic fields in opposite directions are applied to each other, so that the pinned layers of the paired spin valve GMR elements have the same magnetization fixed direction, and the four spin valves GMR that form these pairs. Elements can be formed in one chip. As a result, the entire acceleration sensor can be further reduced in size.

  Further, according to the present embodiment, a closed magnetic circuit is formed by a vertical magnetic field distributed over a wide range by two pairs of permanent magnets, and the spin valve GMR element is disposed in this closed magnetic circuit. Only a minimum magnetic field leaks from the closed magnetic circuit to the outside, and since the leakage magnetic field is reduced, a sufficiently large bias magnetic field is applied. Even when the permanent magnet is downsized, the detection sensitivity of acceleration is stable. In addition, it becomes high and is hardly affected by an external electric field and an external magnetic field.

  Further, according to the present embodiment, since it is not necessary to provide an electrode on the spring member or the magnetic field generating weight member, the wiring structure is simplified. Further, since it has a lower impedance than a piezoelectric element type acceleration sensor or a capacitance type acceleration sensor, it is not easily affected by disturbances.

  In the above-described embodiment, in order to form a closed magnetic circuit, two permanent magnets arranged so that the surfaces facing the magnetic field detection sensor chip have opposite polarities are used. Even when combined with a yoke made of a soft magnetic material, a closed magnetic circuit can be formed.

  In the above-described embodiment, the spin valve GMR element is used as the magnetic field detection sensor, but it is obvious that a TMR element may be used instead.

  Needless to say, the acceleration sensor of the present invention is not only applied to the magnetic disk drive device as in the above-described embodiment, but can be applied to any application for detecting acceleration.

  All the embodiments described above are illustrative of the present invention and are not intended to be limiting, and the present invention can be implemented in other various modifications and changes. Therefore, the scope of the present invention is defined only by the claims and their equivalents.

1 is a perspective view schematically showing an overall configuration of an example of a magnetic disk drive device incorporating an acceleration sensor of the present invention. It is a disassembled perspective view which shows roughly the whole structure in one Embodiment of the acceleration sensor of this invention. FIG. 3 is an exploded perspective view schematically showing a configuration of a spring member, a magnetic field generating weight member, and a magnetic field detection sensor chip provided inside a housing member in the acceleration sensor shown in FIG. 2. It is a figure which shows schematically the structure on the connection on a wiring board in the acceleration sensor shown in FIG. 2, and a magnetic field detection sensor chip. FIG. 3 is a circuit diagram schematically showing an electrical configuration of a wiring board and a magnetic field detection sensor chip in the acceleration sensor shown in FIG. 2. FIG. 3 is an equivalent circuit diagram of the acceleration sensor shown in FIG. 2. It is a figure showing MR resistance change characteristic with respect to the magnetic field angle applied to the lamination surface of a spin valve GMR element. It is a figure explaining the fundamental operation | movement of the strip | belt-shaped leaf | plate spring in the spring member of this invention. It is a figure explaining the operation | movement of the strip | belt-shaped leaf | plate spring which has a fulcrum in the center part and to which the weight member was attached to both ends. It is a figure for demonstrating operation | movement of the spring member in embodiment of FIG. It is a perspective view which shows typically the structure of the spring member and magnetic field generation | occurrence | production weight member in other embodiment of the acceleration sensor of this invention. It is a perspective view which shows typically the structure of the spring member and magnetic field generation | occurrence | production weight member in other embodiment of the acceleration sensor of this invention. It is a perspective view which shows typically the structure of the spring member and magnetic field generation | occurrence | production weight member in other embodiment of the acceleration sensor of this invention. It is a perspective view which shows typically the structure of the spring member and magnetic field generation | occurrence | production weight member in other embodiment of the acceleration sensor of this invention. It is a perspective view which shows typically the structure of the spring member and magnetic field generation | occurrence | production weight member in other embodiment of the acceleration sensor of this invention. It is a perspective view which shows typically the structure of the spring member and magnetic field generation | occurrence | production weight member in other embodiment of the acceleration sensor of this invention. It is a perspective view which shows typically the structure of the spring member and magnetic field generation | occurrence | production weight member in other embodiment of the acceleration sensor of this invention. It is a perspective view which shows typically the structure of the spring member and magnetic field generation | occurrence | production weight member in other embodiment of the acceleration sensor of this invention. It is a disassembled perspective view which shows typically the whole structure in further another embodiment of the acceleration sensor of this invention. FIG. 20 is an exploded perspective view schematically showing configurations of a spring member, a magnetic field generation weight member, and a magnetic field detection sensor chip provided in the housing member in the acceleration sensor shown in FIG. 19. FIG. 20 is a diagram schematically showing a connection on a wiring board and a configuration of a magnetic field detection sensor chip in the acceleration sensor shown in FIG. 19. FIG. 20 is a circuit diagram schematically showing an electrical configuration of a wiring board and a magnetic field detection sensor chip in the acceleration sensor shown in FIG. 19. FIG. 20 is an equivalent circuit diagram of the acceleration sensor shown in FIG. 19. It is a figure for demonstrating operation | movement of the spring member in embodiment of FIG.

Explanation of symbols

10 Magnetic disk 10a Retreat zone 11 HGA
12 FPC
13 Support arm 13a Claw 14 VCM
15 rotation shaft 16 retracted lamp 17 acceleration sensor 18 circuit board 20,190 housing member 20a, 190a wiring board 20b, 190b cover member 21,191 spring member _21a, 171a _1, 171a _2, first strip-shaped plate springs 21b, 21c , 171b, 171c Second strip leaf springs 21d, 21e, 21f, 21g, 191b, 191c Weight support portions 22a, 22b, 22c, 22c ′, 22d, 22d ′, 162a, 162b, 192a, 192b Magnetic field generating weight member 22a ₁ , 22a ₂ , 22b ₁ , 22b ₂ , 22c ₁ , 22c ₂ , 22d ₁ , 22d ₂ , 192a ₁ , 192a ₂ , 192b ₁ , 192b ₂ Permanent magnets 23, 24, 25, 193, 194 Magnetic field detection sensor chip 23a , 23b, 23c, 23d, 24 24b, 24c, 24d, 25a, 25b, 25c, 25d, 193a, 193b, 193c, 193d, 194a, 194b, 194c, 194d Spin valve GMR element 26, 176a, 176b, 196 fulcrum member 80, 90, 191a Spring 81, 91 Support point 82, 92a, 92b Weight member 130a, 130b, 180a, 180b Band-shaped support member

Claims (7)

A spring member for an acceleration sensor to which a magnetic field generating means or a magnetic field detecting means that also serves as a weight member is attached, the first strip leaf spring having a fulcrum at the center portion, and center portions at both ends of the first strip leaf spring Are connected to each other, and the weight members are attached to both ends of each of the second belt springs, and the first belt springs are connected to each other. The strip-shaped leaf spring is configured to generate a bending stress or a torsional stress with respect to an externally applied force to displace the weight member, and the second strip-shaped leaf spring is subjected to an externally applied force. The bending member is configured to displace the weight member with respect to each of the two second strip leaf springs or attached to both ends of each of the second strip leaf springs. Fixed to the weight member, The spring member for an acceleration sensor, characterized by further comprising suppressing planar support member spring action of the second strip-shaped plate spring. A housing member, four magnetic field generating weight members, a spring member having a fulcrum attached to the housing member, and at least three of the four magnetic field generating weight members are attached to the housing member, respectively. At least three magnetic field detection sensors, wherein the spring member includes a first strip leaf spring having the fulcrum at the center portion, and a center portion connected to both ends of the first strip leaf spring. And the four magnetic field generating weight members are attached to both ends of the two second belt springs, respectively, and the first belt springs are external. The second belt spring is configured to bend with respect to an externally applied force. By generating a force which is configured to displace the magnetic field generation members with weights, it said attached to both end portions of the two second or each strip-shaped plate springs respective second strip-shaped plate springs wherein 4 An acceleration sensor characterized by further comprising a belt-like support member that is fixed to two of the two magnetic-field-generating weight members and that suppresses the spring action of each second belt-like leaf spring. . The magnetic field detection sensor includes a magnetization fixed layer and a magnetization free layer, and the magnetization fixed layer is at least one pair whose magnetization is fixed in a direction parallel to a displacement direction of the first strip-shaped leaf spring or the second strip-shaped leaf spring. And the magnetic field generating weight member includes at least one permanent magnet, and when the external force is not applied, the at least one pair of multilayered magnetoresistive elements is stacked. The acceleration sensor according to claim 2 , wherein a magnetic field is applied in a direction substantially perpendicular to the surface. The acceleration sensor according to claim 3 , wherein the at least one permanent magnet includes a pair of permanent magnets arranged in parallel so that surfaces facing the magnetic field detection sensor have opposite polarities. 5. The acceleration sensor according to claim 4 , wherein the at least one pair of multilayered magnetoresistive elements are arranged to face the pair of permanent magnets, respectively. 6. The acceleration sensor according to claim 3, wherein each of the multilayered magnetoresistive elements is a giant magnetoresistive element or a tunnel magnetoresistive element. A magnetic disk drive apparatus characterized by comprising an acceleration sensor according to any one of claims 2 to 6.

Images